llvm-objdump bug may hide single byte instructions near a label.

[srking]

Summary

An off-by-one bug in calculating the distances between labels can hide small instructions. This bug is in target independent code.

This is my first patch submission, so hopefully no major bungles.

[srking]

Resubmitting with proper Phabricator fields.

test/Object/objdump-label.test

+RUN: llvm-objdump -d %p/Inputs/trivial-label-test.elf-x86-64 \
+RUN:              | FileCheck %s -check-prefix ELF-x86-64
+
+ELF-x86-64: file format ELF64-x86-64
+ELF-x86-64: Disassembly of section .text:
+ELF-x86-64: foo:
+ELF-x86-64:        0: 90                                            nop
+ELF-x86-64: bum:
+ELF-x86-64:        1: 90                                            nop
+

tools/llvm-objdump/llvm-objdump.cpp

for (const SectionRef &Section : Obj->sections()) {
     StringRefMemoryObject memoryObject(Bytes, SectionAddr);
     uint64_t Size;
     uint64_t Index;
 
     std::vector<RelocationRef>::const_iterator rel_cur = Rels.begin();
     std::vector<RelocationRef>::const_iterator rel_end = Rels.end();
     // Disassemble symbol by symbol.
     for (unsigned si = 0, se = Symbols.size(); si != se; ++si) {
+
+      // The end is either the section end or the beginning of the next symbol.
+      // If this symbol has the same address as the next symbol, then skip it.
       uint64_t Start = Symbols[si].first;
-      uint64_t End;
-      // The end is either the size of the section or the beginning of the next
-      // symbol.
-      if (si == se - 1)
-        End = SectSize;
-      // Make sure this symbol takes up space.
-      else if (Symbols[si + 1].first != Start)
-        End = Symbols[si + 1].first - 1;
-      else
-        // This symbol has the same address as the next symbol. Skip it.
+      uint64_t End = (si == se - 1) ? SectSize : Symbols[si + 1].first;
+      if (Start == End)
         continue;
 
       outs() << '\n' << Symbols[si].second << ":\n";
 
 #ifndef NDEBUG
       raw_ostream &DebugOut = DebugFlag ? dbgs() : nulls();
 #else
       raw_ostream &DebugOut = nulls();